High explosive devices such as, for example, artillery shells, bombs, rockets and other weapon warheads, must be capable of being handled safely under conditions of considerable stress and shock while at the same time be capable of reliably detonating at a predeterminable time before, during or after impact with the desired target. For convenience of reference, the word "weapon" as used herein is intended to include all forms of explosive devices, as for example but not limited to those listed above.
Most weapons employ a fire train for detonating the main explosive charge, that is, one or more progressively larger explosive devices which are detonated by a fuzing mechanism and which culminate in exploding the main powder charge. For example, an initial small explosive charge, often called a detonator is ignited by a firing pin or firing circuit. This initial small charge in turn ignites the main charge either directly or through one or more intermediate booster explosive charges. This sequence of charges is referred to as the fire train. As used herein, the word "fuze" is intended to refer to the combination of a fire train and its activating mechanisms or devices, and including any safe and arm mechanism or devices. A fuze may be located in the nose or base or elsewhere in the weapon, or there may be fuzes in multiple locations in the weapon, depending upon the user needs.
A "safe and arm" device is a mechanism which renders the fuze inert ("safe") while the weapon is being transported or handled so that it will not explode (even under shock conditions which would ordinarily set it off), and which, after the weapon is launched toward its target, turns on ("arms") the fuze so that subsequent activation thereof causes the weapon to explode.
In order to satisfy the conflicting requirements of safety and reliable detonation on target, it has been common in the art to employ out-of-line safe and arm devices as a part of the fuze which activates the weapon. An out-of-line safe and arm device is one in which a physical barrier is located in the explosive fire train to interrupt or physically block the detonation process of the fire train when the weapon is intended to be in the "safe" condition and removed therefrom when the weapon is intended to be in the armed condition. Various mechanisms are known in the art for accomplishing this.
A difficulty arises in employing conventional fuzes, such as is illustrated in FIGS. 1-2, when the weapon is intended to be used against hardened targets, as for example, targets protected by many feet or more of reinforced concrete or successive concrete walls separated by filled or empty regions. While conventional hard-target weapons (e.g., bombs, rockets or shells) may be capable of penetrating such reinforced structures, prior art fuzes have not always been able to provide reliable detonation timing following penetration. When attempting to destroy a bunker which may consist of successive chambers each separated and protected by reinforced concrete, it is highly desirable to be able to time detonation of the fuze so that the weapon reliably explodes in a particular location, e.g., after having penetrated through very massive reinforced concrete walls or a predetermined number of reinforced concrete walls and/or spaces.
Accordingly, there continues to be a need for an improved means and method for detonating explosive charges, especially for a fuze exhibiting great shock tolerance and at the same time providing out-of-line safe and arm capability.